core: exit does not dereference device pointers when logging

Device pointers that wrongly remain in the referenced device list could
point to already freed memory. Dereferencing them for the purpose of
logging devices related data could lead to segmentation faults
or inaccurate information

libusb/core.c

@@ -2626,11 +2626,8 @@ void API_EXPORTED libusb_exit(libusb_context *ctx)
 
 	usbi_io_exit(_ctx);
 
-	for_each_device(_ctx, dev) {
-		usbi_warn(_ctx, "device %d.%d still referenced",
-			dev->bus_number, dev->device_address);
-		DEVICE_CTX(dev) = NULL;
-	}
+	if (!list_empty(&_ctx->usb_devs))
+		usbi_warn(_ctx, "application left some devices referenced");
 
 	if (!list_empty(&_ctx->open_devs))
 		usbi_warn(_ctx, "application left some devices open");